The present invention relates to a method for avoiding an unwanted collision between a tool and a workpiece in a machine tool. The invention also relates to a facility for controlling a machine tool.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
When machining workpieces using machine tools it is important to avoid unwanted collisions between the tool and the workpiece, which may result in destruction of the tool and/or workpiece. If the running of a parts program which controls the movements of the machine tool is interrupted, particularly in the middle of the program, and the tool is moved manually away from the workpiece and then moved manually back to the original position to continue the program, unwanted collisions can frequently occur between the tool and the workpiece, since, to bring about the movement predetermined manually by the operator, the machine axes operate with so-called associated interpolation with the result that a number of machine axes are moved at the same time to move the workpiece and/or tool, so the operator often finds it difficult to estimate how a manually input predefined movement will be implemented by the machine tool. Machining on the machine tool, which often continues for a number of hours or even days, would then be to no avail, as after the collision the workpiece is no longer usable.
Conventional approaches are known wherein a collision avoidance system, with which, while a workpiece is being machined, uses a simulation to calculate a workpiece model to bring about collision avoidance. However, the calculation of a workpiece model requires a great deal of computation time, so that on the one hand a high level of computation capacity is required to implement such a collision avoidance system and on the other hand it is necessary, before the actual machining of the workpiece can be started, for the simulation to run some time before actual workpiece machining starts, since it is generally not possible to perform the determination of the workpiece model at the same time as the actual machining of the workpiece, despite the high computation capacity. In practice this means that when the operator presses the start button for machining, nothing happens initially at the machine tool, as the machine tool first has to take a certain time beforehand to calculate the current geometric workpiece form resulting during the machining of the workpiece by the tool, i.e. the workpiece model. This increases the machining time for the workpiece. Also relatively large safety gaps are required between workpiece and tool, in particular for manual operation.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for avoiding an unwanted collision between a tool and a workpiece in a machine tool and a facility for controlling a machine tool, which allow a short workpiece machining time.